CBSE Class 11 Chemistry Chapter 3 Notes: Classification of Elements and Periodicity in Properties
In this chapter, we will discuss the development of the periodic table and the periodic law. The arrangement of elements in the modern periodic table is organized into eight vertical columns (groups) and seven horizontal rows (periods) based on their atomic number.
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Based on the electronic configuration, elements can be classified into four types in the periodic table, viz s-block, p-block, f-block, and d-block elements. More than 70-80% of the known elements are metals. Elements located at the top of the periodic table are nonmetals and are less than 20. In a group, as the atomic number increases, the metallic character increases. In a period, there is a decrease in the metallic character from left to right. Also, the chemical, as well as the physical properties, vary with their atomic number. Elements of the same group exhibit similar chemical properties because of the similar valence shell electronic configuration.
Periodic Trends In Properties Of Elements
- Atomic sizes – With the increase in atomic number the atomic radii in the group will increase. On the other hand, the atomic radii decrease from left to right in a period.
- Ionization enthalpies – Decreases down a group but increases across a period.
- Electron gain enthalpies – Tends to become less negative down a group and more negative across a period.
- Electronegativity – Electronegativity decreases down a group but increases across a period.
- Chemical reactivity – Chemical reactivity is lowest in the centre and is highest at the two extremes of a period.
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Few Important Questions
- What is the difference between Modern Periodic Law and Mendeleev’s Periodic Law?
- What is the ionic radius? What is the atomic radius?
- What is isoelectronic species? Give an example.
- Elements in the same group have similar chemical and physical properties. Why?
To discover more about this chapter, go through Class 11 Chemistry Chapter 3 Notes from BYJU’S.
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Frequently asked Questions on CBSE Class 11 Chemistry Notes Chapter 3: Classification of Elements and Periodicity in Properties
How many elements are present in the periodic table?
A total of 118 elements are present in the periodic table.
What is the meaning of ionisation enthalpy?
The enthalpy change associated with the removal of the original electron from an atom with a single gas in its ground surface is called as the first ionization enthalpy.
What are the d-block elements?
D block elements are the elements that can be found from the third group to the twelfth group of the modern periodic table. The valence electrons of these elements fall under the d orbital. D block elements are also referred to as transition elements or transition metals.